Plate-and-gasket style heat exchangers are known, typically in the form of stacks of metallic plates having an elastomeric circumferential seal between two adjacent plates. The plates are usually stacked directly against each other, with the resulting plate stack being inserted between two thicker end-plates. The mechanical strength required to make the stack tight is generally provided by through-rods with adjustable nuts on one or two threaded ends, providing a compressive force to the stack via the end plates.
This type of stack construction is suitable for metallic or similarly flexible plates, and particularly for heat exchangers. Thanks to the generally high elasticity of metal and its resulting ability to withstand deformation without damage, metallic parts can deform slightly to cope with non-perfect alignment and/or thickness differences while maintaining a tight seal without risk of breaking. In addition, in heat exchanger applications, a tight seal is not strictly necessary in the interior of the plates. This is because a heat exchanger is not very sensitive to the effects of poor interior wall sealing, such as poor residence time distribution, dead zones and/or by-pass paths. Ultimately, such defects caused by poor internal wall sealing will just reduce slightly the overall heat exchange performance, and this can be compensated by an increase in the heat exchange surface area.
For example, DE19617396 describes a stack of plates with sealing using a peripheral elastomer gasket. The gasket is placed in a groove, or can be potentially directly formed in the groove by injection. The plates may be made of metal or graphite, both of which have flexibility much higher than ceramic or glass materials.
In DE102006009791 is disclosed a stack of ceramic plates sealed in part with O-ring gaskets inserted in a rectangular groove located close to the edges of the plates. The groove is so designed that it can contain all the O-ring volume after compression, and the plates are compressed to physically rest on each other, purportedly to minimize the mechanical stress resulting of the compression of the stack and to avoid any fluid by-pass between separate fluid paths by fluid traveling in any unintended gap that may remain between the two plates that can occur when there is any gap remaining between the facing surfaces of two adjacent plates. Where plates are somewhat rough or slightly warped, sealing by direct-contact compression between the surfaces of the plates imposes stresses that may be too much for materials such as glass and ceramic.
In US20110165033 is described a stack of ceramic plates with a flat gasket formed of resilient or compressible material to ensure the tightness between plates. This structure is intended to cope with the distortion of the ceramic plates (the distortion present before stacking) without any risk of breakage. The proposed solution has, however, many disadvantages. With the use of a flat gasket, the level of pressure required to seal the assembly is significantly higher that the pressure of the fluid within the device (a value about five times higher is indicated in the patent document) leading to constraints on the design of the ceramic plate. Further, due to such high compression pressures, the assembly will also be very sensitive to any perturbation(s) due to ageing, temperature variations, and other variations over time, particularly if an individual stack includes more than the total of four plates shown in the example of the patent. Still further, due to the high compression pressure, the gasket will not resume its original shape upon removal from the assembly, making the use of a new gasket mandatory after each disassembly, leading to additional cost for the end user. Although it may be good practice in some processes to replace a gasket after every disassembly, some other gaskets (O rings for example) are much more tolerant and can, in practice, in appropriate cases, be re-used several times. Still further, as seen from the patent figures and description generally, the particular gasket design is closely tied to the particular flow pattern or plate design with which the gasket cooperates. Thus the presented gasket embodiment can be applied only with a specific plate design, and any changes in the fluidic design require significant changes in gasket design, and complex fluidic channels would require complex gasket shapes.
There is then a need to find a specific, reliable, and reasonably cheap solution for non-permanent (“disassemblable”) sealing of a plate-type continuous flow reactor having plates of ceramic and/or glass material.